Interface of posts partly non-responsive

I am having trouble when I want to edit a post. I can type text in the main area and the exerpt, and the toolbar is mostly working. However, the fields underneath (like exerpt, slug, etc.) I cannot collapse or foldout. Neither the field on the right with tags, categories etc. Putting a hyperlink in the text also does not work (I cannot open it for more features or to select a link from my site). Moreover, I cannot access the post in text mode.
I had a look on my pages, and there everything appears to work fine.
Am I overlooking something/doing something wrong/installed somwthing wrong?

Thanks!